When we humans make a mistake, we have an instinctive "oops" reaction in our brains: a spike of negative voltage in the medial-front cortex. While this is something that has been observed by scientists, the reason why was a little more unclear.

To examine what effect this mistake response has on our behavior, two psychologists from Vanderbilt University in Nashville, Tennessee -- Ph.D. candidate Robert Reinhart and assistant professor of psychology Geoffrey Woodman -- designed a cap that administers a low-level current to the brain to simulate the spike. They hypothesized that the spike plays a role in learning, allowing the brain to learn from mistakes.

Vanderbuilt University

"That's what we set out to test: what is the actual function of these brainwaves?" Reinhart said. "We wanted to reach into your brain and causally control your inner critic."

The cap secured two saline-soaked sponges to the test subject's head, one to the cheek and one to the crown. Through these sponges, the researchers applied 20 minutes of transcranial direct current stimulation (tCDS) -- one of the safest ways to non-invasively stimulate the brain.

They applied three types: anodal (from the crown to the cheek); cathodal (from the cheek to the crown); and control, which replicated the physical tingling sensation of tCDS without applying the current.

The subjects were then given a learning task with a high chance of making mistakes. They had to figure out by trial and error which buttons on a game controller corresponded to colors displayed on a monitor. This was complicated by occasionally showing a signal indicating the subject was not to respond. For even more difficulty, participants had less than a second to respond correctly.

While the subjects were undertaking this task, the researchers monitored their brain activity to gauge how the brain reacted to mistakes in the moment, and observe how this activity changed under the influence of the tCDS. They found that under an anodal current, the negative-voltage spike was almost twice as large as normal, and significantly higher for 75 percent of the subjects.

Their behavior was also altered, unknown to the subjects: They made fewer mistakes and learned from their mistakes more quickly than they did under the control. Under the cathodal current, the effect was the opposite -- a smaller spike and more mistakes. The effect of the 20-minute tCDS was also transferred to other tasks, and lasted about five hours.